Pyrolysis of hydrocarbons to produce olefines



' also to provide a the carbon is decreased. I have discovered that by certain pretreatment of the alkaline earth oxide catalystby controlled Patented Apr. 15, 1947 UNITED' STATES.

PYROLYSIS or nrnaocnnaons 1'0:

PRODUCE OLEFINES John H. Haslam, Louisville, Ky., assignor to The Girdler Corporation, Louisville, Ky. a corporation of Delaware No Drawing. Application February 29, 1944,v Serial No. 524,464-

ized, usually mixed with an inert gas such as steam or nitrogen, and then passed over the catalyst at an elevated temperature. Under proper conditions, a portion of the hydrocarbon is converted into the desired olefine, and there is also other decomposition products. posed cyclohexane. could. be separated from the butadiene and other decomposition products, and

- recirculated OVerthe catalyst.v Carbondeposited at such a ratethat after 2 hoursoperationthe catalyst was coated withicarbon, which comprised 0.5% by weight. of. the; catalyst. As the deposition. of carbon continues, the butadiene' yield. -de-' creases, and; in a. comparativelyshorttimethe produced. free carbon and a mixture of other untubes become pluggedwithcarbon.

desired decomposition products. The carbon so .formed deposits in the reaction chamber and.

often accumulates to the point where it blocks the chamber and coats the catalyst'so as to pose of olefine production. When this condition is reached, the operation has to be stopped and. the catalyst changed ortreated in situ by oxidation to remove carbon. This is a costly and timetion of such carbon and other decomposition product is the result of an undesired reactionand. results in a loweryield of the desired olefine.

In an effort to' discover some means for re pressing the depositionof carbon: on the catalyst, and also i in an effort: to discover some means of increasing the butadiene' yield, a series of tests (quickly render it no longer efiective for the vpurhave'been made to determinethe effect of preheatin p thercatalyst on these factors,.'and the results are shown in. the followingtable;- In obgiven are those obtained by a single. passing of .eonsuming operation. Furthermore, the produc- 2o cyclohexane over the catalyst, calcium oxide, at

a temperature of 650 C.,. and after-the-catalyst had been preheate'di to the temperatures and'for. the times stated.

Per cent of Per cent or 3 Per canto! Time 01 Tam r Carbon on Per cent of Butadienein Cyclohexane Pretum g f C t I t v -Cyolohexane Products of oonvertodito beating, heating'ea 2 5 decomposed DEOOXDOSL butadiene Hrs. I 2.0 Hm (by weight) tivrgighty (by weight) I 1 i 4 I 22 200 0. 9 12. 6 24. 6 3- 10 22 400 0. 5 17. 8 '17. 8 3. 17- 6 875 O. 4 7. 3 20.7 1a 51 4 1,100 0.0 0 18.0 0-72 Obviously, it is desirable to providea process in which the. yield of theolefine is'in'creased, and

heating, I can accomplish these desired results.

' at 500 space velocity. By space velocity" is From the data given in thistabledt willbe seen that when the catalyst. was preheated to 875 C. process. in which the deposit of to 199 (1., the carbon deposit on thecatalyst was -.--'-'-'=""alin t entirely or entirely eliminated, but thepyrolysis of-cyclohexane. the deposition of car-.

bon on the catalyst-was eliminated, but theactivmeant the volume of gas under standardcondiity of the catalyst was reduced-to such an extent tions of temperature and pressure, introduced per hour per volume of catalyst; As a result, 10% of the cyclohexane was decomposed. 23% of the cyclohexane that was decomposed formed butadiene, and'theother 77% formed carbon and vsirable effect oillargely'eliminatingcarbon deposi that only 4% of the cyclohexane was decomposed,

and of that, only 18% was. butadiene. Therefore,

The und'ecompercentage of cyclohexane WhiChWflS decomposed was decreased, and the percentage 01' the decom' position product which was the desirable buta- A procedure following the teachings of the 45 diene, was somewhat decreased It will be noted prior art is one in which cyclohexane vapors are tion but the undesirable eilect or reducing the yield of butadiene. The latter is not so important, as the undecomposed cyclohexane may be recycled.

n will also be noted that when the catalyst was preheated at 200'? C. for 22 hours, and then vention the calcium oxide is preheated in a 2-.

stage heating process, although in carrying out the invention, either stage may be used alone, de-

' pending upon the results desired. In the first stage the calcium oxide ishe'atedior at least one hour to a temperature above that at which it is to be used in the pyrolysis reaction, and in the claim as new and desire to secure by Letters second stage it is held at a temperature below that at which it is used in the pyrolysis-reaction for at least iourhours.. What changes are ei- Jected in the calcium oxide in these preheating stages is not known,- but tests show that by these preheating steps,'lesscarbon deposit is obtained and higher yields oi butadiene are obtained. -fi One way in which this invention has been carried out is as follows: The catalyst was preheated in two stages, .while a gas such as nitrogen, oxygen; 'or other gas; which was inert so far asaction on the catalyst was concerned, was passed.

over it. The preheating in the first stage was to a temperature of -1100-C. for a period such as2 hours, andthen the temperaturewas maintained in the second stage at about 200 C. for a longer period, such .as 22 hours. The "changes effected in the catalyst were of such a character that when the catalyst was used at650 C. for pyrolysis or cyclohexane, satisiactory'results were obtained.

In one such test 8.9% of the 'cyclohex'ane was converted to'decomposition products containing 38.1%.0! butadiene, and with substantially no deposition oijcarbon on the catalyst. 39.1% of the 8.9% gave a yield oi. 3.48%..as against a maxlthough calcium oxide is the catalyst em- I vlvloycd in the tests above reterred to, it will be apparent that the same preheating treatment may I be applied to advantage with other alkaline earth oxide cataylsts used for this type at reaction, and that pyrolysis of other hydrocarbons may be effected to produce other olefines.

Having thus described my invention, what I Patent is:

, l. The process of securing a decrease of carbon deposit on a catalyst'composed essentially oi an alkaline earth oxide; and du'ringpyrolysis of a hydrocarbon to form an oleflne, which includes preheating the catalyst for more than one hour to a temperature above that at-which pyrolysis is to be effected but not substantially above 1300 C;, and then passing the hydrocarbon-over the catalyst at the pyrolysis temperature and without intermediate cooling below the pyrolysis. temperature. p r

2. The process oi producing an oleflne. by pyrolysis of a hydrocarbon in .the presence of a catalyst composed essentially of an alkaline earth oxide, and eflectingreduction in the deposit oicarbon during said pyrolysis, which'includes pro-'- heatlngs'aid catalyst for at least an hour'to a temperature above that at which pyrolysis is to be effected and to at least 850 C. but not substantially above 1300" C., anddirectly thereafter passing the hydrocarbon over said catalyst at the pyrolysis temperature. l

3. The process of effecting p rolysis of cyclohexane to butadiene and reducing carbon deposition during said pyrolysis. which includes J preheating a catalyst composed essentially of calcium oxide for at least one hour at a temperaturebetween 850 C. and 1300 0., and directly thereafter passing the cyclohexane over the catalyst at'the pyrolysis temperature.

4. The process of increasing the yield of the oieflne in the py olysis or a hydrocarbon in the imum oi 3.17% shown in the table. The higherypercentage of butadiene inthe decomposition productsis obviously more important than a high percentage 0! cyclohexane decomposed, because the-undecomposed' cyclohexane is separated from other decomposition products after each pass, and

is recycled over the catalyst. Tests indicate that the high initial preheating o! the catalyst should be to temperatures above 850 C but not above 1300 C. As the time of preheating at850 C. is.

increased, the operation oi thecatalyst in use is improved, and as the temperature of preheating is increased above 850 0., shorter preheating times are required. Tests indicate that the later holding at a low temperature should be between 100 C. and 400 C. for more than 4 hours.

The best results seem to be by using a tempera- 'ture between 1000' C. and 1200 C. for 2 t0 4 hours inthe first stage, and a temperature of about i ,200' 'C. for about 20 hours in the second stage.

'The above ranges or temperature and time are suggested as suitable operating ranges, though I do not limit-myself to these conditions, since the invention is of a broader nature. and either heating'stage may be used alone; The treating or a catalyst at high temperatures is important for obtaining certain advantages and the treatment or the catalyst'rat lower temperatures is important 1o!obtainingotheradvantages.

presence 0!; a catalyst composed essentially of an alkaline earth oxide, which includes preheating said catalyst for more than four hours at 'a temperature above 100' C. and below that at which pyrolysis is .to be effected, directly thereafter heating the catalyst to the temperature at 'which the pyrolysis is to be eflected and passing thehydrocarbon over the catalyst.

5. The process of producing an oleflne by pyrolysis of a hydrocarbon in the presence of a catalyst composed essentially of alkaline earth oxide, and effecting increase in the yield of oleiine, which includes preheating said catalyst for a' period of at least four hours to a temperature below that at which pyrolysis is to be eflected and within the range of about 100 C. to about 400 C..

' and then passing the hydrocarbon oversold catalyst at the pyrolysis temperature and without intermediate cooling of the catalyst below said preheat temperature range. 6. The process of eilectlng pyrolysis of cyclo-l hexane to butadiene and securing increased yield a temperature range.

01' butadiene, which includes preheating a cata-; lyst composed essentially of calcium oxide for 7 about twenty hours at a temperature below that at which pyrolysis is to be effected and'within the range of about C. to about 400 0., and then passing the cyclohenaneover said catalyst at the pyrolysis temperature and without inter-' mediate cooling of the catalyst below 'saidpreheat '7. The process oi producing an oleflne by the pyrolysis of a hydrocarbon in the presence oi-a 5 catalyst composed essentially 01' an alkaline earth oxide, which includes preheating said catalyst for a period of at least one hour at a temperature above that at which pyrolysis is to be effected but not substantially above 1300 C., then holding the catalyst for a period or at-least four hours at a temperature ofat least 100 C. but below that at which pyrolysis is to be effected, and directLv thereafter heating the catalyst to a temperature at which pyrolysis is tobe effected and passing the hydrocarbon over the catalyst.

8. The process of producing an olefine by pyrolysis of a hydrocarbon which includes preheating a catalyst composed essentially of an alkaline earth oxide at ajtemperature above 650 C. but not substantially above 1300 C. for at least one hour, then preheating said catalyst at a temperature of at least 100 C. but not substantially above perature range of said second preheating step,

to thereby produce the butadiene, by pyrolysis of the cyclohexane.

11. The process which includes preheating a u "said catalyst to cool to a temperature within the 400 C. for at least four hours, and then passing the hydrocarbon over the catalyst at a pyrolysis temperature of about 650 C. but without intermediate cooling of the catalyst below said last mentioned preheating range.

9. A process which includes preheating a catalyst composedlessentially of an alkaline earth oxide, to a temperature between 850 C; and 1300 C. for more than one hour, then holding said catalyst at a temperature between 100 C. and 400C. for more than four hours, and directly thereafter heating the catalyst to a pyrolysis temperature of over 400 C. and less than 850 C. and passing a hydrocarbon over the catalyst at the pyrolysis temperature to produce an olefine by pyrolysis of the hydrocarbon.

10. The process of producing butadiene, which includes preheating a catalyst composed essentially of an alkaline earth oxide, at a temperature above 650 C. but not s bstantially above 1300 C. for at least om hour, then heating said catalyst at a temperature of at least 100 C. but

, below 650 C. for at least four hours, and then passing cyclohexane. over the catalyst at a pyrange of 100 C. to 400 C., and holding it in that temperature range for more than four hours. and directly thereafter heating the catalyst to a pyrolysis temperature of over 400 C. and less than 850 C. and passing cyclohexane over the catalyst to produce butadiene by pyrolysis of the cyclohexane, Y

12. The process of effect ng Pyrolysis of cyclohexane to butadiene, which consists in heating a catalyst, composed essentially of calcium oxide, to a temperature of about 1100 C. for about two hours, then holding said catalyst at about 200 C. for about twenty hours, and directly thereafter heating the catalyst to a pyrolysis temperature of about.650 C. and passing the cyclohexane thereover.

JOHN H. HASLAM.

- file 0f this'patent:

rolysis temperature of about 650 0. without intermediate cooling of the catalyst below the tem- UNITED s'rA'rEs PATENTS Number Name. Date 2,274,988 Matuszak Mar. 3, 1942 2,279,198 Huppke Apr. '7, 1942 FOREIGN PA'I'ENTS Number Country Date 307,945 British Mar. 11, 1929 OTHER REFERENCES Thorpe, "Dictionary of Applied Chemistry, vol. I, p. 732 (1 pge). Longmans, Green 8: Co., New York (1921), (Patent Oiiice Library.) 

